The present invention relates to a sealing device, and in particular to a sealing device such as a seal and an oil seal used for sealing rolling apparatuses including a rolling bearing, a linear guide apparatus and ball screw.
Conventionally, the lip of the sealing device used for the applications described above has been most generally made of rubber material compositions mainly comprising NBR (acrylonitrile-butadiene rubber) taking oil resistance into consideration.
In cases where heat resistance and chemical resistance are required, those material compositions which mainly comprise an acrylic rubber, a silicone rubber or a fluorine-contained rubber (FKM) have been used.
However, the sealing devices using the conventional rubber material compositions described above had the following drawbacks.
In recent years, the number of revolution has increased for the principal spindle of machine tools and, as for tools in general, highly heat-resistant materials as well as heat-resistant coating technologies have been developed to a noticeable degree. Accordingly, cutting works are conducted at an ever-increasing speed and efficiency.
To cope with these advances, the cutting lubricant used in cutting work is required to be provided with the highest level of cooling capability absorbing the enormous amount of heat generated in the vicinity of the cut point, the permeability with which the oil can instantaneously reach the cut point, and a lubricating property for the cut point of an elevated temperature and a high pressure. To meet these requirements, soluble-type synthetic cutting coolants are recently being used instead of the conventional emulsion-type cutting lubricants.
The soluble-type synthetic cutting coolant, which can be subjected to waste water treatment due to its perfect solubility in water different from the emulsion-type cutting lubricant, has the most prominent advantage of a high permeability as a result of incorporation of a variety of additives such as amines in a large quantity. Accordingly, such a soluble-type synthetic cutting coolant exhibits a high permeability toward rubber materials, too.
Machine tools include a number of sealing devices and oil seals for rolling apparatus such as rolling bearings and linear guide apparatus. These sealing devices are brought into contact with the cutting lubricant during cutting works. When the lip made of a rubber material composition of the sealing device contacts with the cutting coolant mentioned above, the cutting coolant causes the lip material to swell and soften due to its high permeability. Thus, the mechanical strength of the lip may be deteriorated. In the case of a contact-type sealing device, an exposed thread of the seal expands and promotes wearing, resulting in the deterioration of sealing property, which may lead to a reduced life of the machine tool itself.
In the case where the rubber is FKM (a vinylidene fluoride-hexafluoropropylene-based fluorine-contained rubber or a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluorine-contained rubber), hydrogen fluoride (HF) is eliminated from the vinylidene fluoride moiety amply present in the rubber structure by the action of the amine-based additives. Such a reaction may probably lead to the decomposition of the rubber accompanying the deterioration of its mechanical strength.
Generally speaking, sealing devices are composed of a rubber-made member made of a rubber material composition, and a reinforcing member such as a metal mandrel for the rubber part wherein the two members are integrally bonded together. The various additives such as amine-based additives in the cutting lubricant may attack and modify the adhesive used to bond the rubber-made member to the reinforcing member. Then, the adhesive strength may probably be weakened to lead to the separation of the two members.
As an actual example, when a sealing device in which the rubber-made member comprises a nitrile rubber and bonds to a metal mandrel by means of vulcanization adhesion with use of a phenol resin-based adhesive is immersed in an aqueous dilution of the soluble-type synthetic cutting coolant for a long time, the adhesive was attacked in addition to the swelling and softening of the rubber itself, and in some cases the rubber-made member is entirely separated off from the metal mandrel.
It is also anticipated that a similar problem may occur for such sealing devices used for machinery and tools that may contact with antifreeze solutions and engine oils for automobiles since these fluids also contain a large amount of additives such as amine-based additives that have an adverse effect on rubbers.
Hence, the object of the invention is to solve the above-described problems associated with the conventional sealing devices, and to provide a sealing device operating for a long life without suffering from deterioration even when used in an environment where the sealing device is in contact with various chemicals including cutting lubricants containing additives having an adverse effect on rubbers.
To achieve the object described above, the invention is constructed as follows. According to the invention, in a sealing device equipped with a lip made of a rubber material composition, the rubber material composition is characterized by comprising 100 parts by weight of a tetrafluoroethylene-propylene copolymer and 0.02 to 10 parts by weight of an ethylene-propylene-based copolymer.
Since such a constitution is provided with an excellent chemical resistance against various additives such as amine-based additives and thus stands well spoilage, the sealing device can operate for a long life even when used in an environment where chemicals including cutting lubricants containing the above described various additives contact therewith. Correspondingly, the machinery and tools equipped with the sealing device of the invention can enjoy a long life.
The sealing device of the invention may have a structure comprising an rubber-made member comprising the above described rubber material composition (including a lip) bonded to a reinforcing member that reinforces the rubber-made member. There is no restriction on the shape of said reinforcing member so long as the reinforcing member made of a metal or a plastic can impart a sufficient strength to said sealing device.